This invention relates to structure for controlling the amount of effort required to actuate the steering levers of an earth moving vehicle, and more specifically, to a mechanism that increases or decreases the forces placed on the levers to allow an operator to more accurately steer the vehicle.
Movement of vehicles of the type including skid-steer loaders is typically controlled by an operator""s actuation of a pair of handles or levers located near the operator""s seat in the vehicle. Each of the levers operating together control either forward or rearward motion of the vehicle, i.e., to move in a forward direction, an operator needs to push both levers forward at the same time and vice versa with regard to movement in the reverse direction. If an operator is moving in a forward or reverse direction and unexpectedly releases one of the levers, it may quickly return to its neutral and upright position without permitting an opportunity for the operator to regain its control. As a consequence, the vehicle will cease to move in the desired direction and often be abruptly jerked toward either a left hand turn if the left lever is released or a right hand turn if the right lever is released.
The above movement caused by actuation of either or both of these levers is permitted through their connection with a pair of rotating sleeves which are mounted to and which revolve around a steering shaft that extends therebetween. Connected with the sleeves are separate steering linkages which attach the sleeves to both a left and right pump for controlling movement of the vehicle towards either a left or right direction. The pumps are actuated by movement of the levers to release fluid to hydraulic motors which are driven or powered by the pumps. Each of these motors then drives a plurality of wheels or other traction device attached with the vehicle to propel it along the ground surface. Accordingly, upon movement of either one or both of the levers, the operator may cause the vehicle to travel in a desired direction as some effort or force is applied by the operator to reposition one or both of the levers either away from or towards the neutral position. In doing so, however, the operator will encounter a certain amount of resistance in moving the levers from the neutral position.
Resistance is a measure of the force applied to the levers when opposition to movement thereof is encountered. It is also that which determines the pace at which each lever returns to its neutral position after it has been moved therefrom. Resistance has been controlled by a separate mechanism mounted to and cooperating with the left pump and another with the right pump. Each mechanism has included a mounting plate attached to the left and right pump individually. This mounting plate has included a top and bottom portion with the bottom portion being mounted to the pump. On an interior of the top portion, a slide plate, the purpose of which is described below, has been secured thereto. With the top portion and slide plate secured together, the set has been thereafter mated with the bottom portion for movement on guide rails or pins that extend between the two portions so as to allow the set to glide therealong. Extending through a first side of the mounting plate, a bolt around which a spring has been placed has been used to provide resistance at each of the levers. To apply a desired amount of pre-load, and thus resistance at each of the levers, screws have been secured to the slide plate on a side thereof to allow an operator to set the amount of distance that exists between the slide plate/top portion of the mounting plate combination and the back portion of the mounting plate when each lever is in the neutral position. Setting of this distance has been made by the operator securing the slide plate relative to the first side of the mounting plate through the use of the screws so as to adjust the amount of pre-load described above.
To stroke the pumps and therefore allow hydraulic fluid to flow to each motor, each of the steering linkages has been connected to an arm extending from the left or right pump that has been used to permit the pumps to be stroked upon movement of the levers. Specifically, each arm has included a roller assembly on an end thereof that is positioned to initially contact the slide plate under the pre-load set above when a particular lever is in the neutral position and which further pushes against the slide plate when the arm is re-positioned by movement of the lever to either the forward or reverse direction. Further compression of the spring then takes place as the roller contacts its slide plate. This compression of the spring thereby increases the resistance at the effected lever(s). As a consequence of applying additional pressure against the slide plate in either the forward or reverse direction, movement of the arm strokes the pump and causes hydraulic fluid to flow to the respective left or right motor to allow the traction device of the vehicle to propel it in the desired direction.
Use of the above adjustment mechanism, however, carries with it at least five disadvantages. First, achieving the same resistance at each of the levers at the same time is problematic since there are two separate mechanisms used to obtain resistance at each of the left and right levers. Such a problem arises because each mechanism uses its own spring having a separate manufacturer""s preset constant determinative of the force required to place the spring in either tension or compression. Because of this, an operator is left to judge and compensate for how much force should be used to actuate one or both of the levers. To have to do so is inconvenient and bothersome to those wanting a similar amount of effort or force to be required to move each lever out of its neutral position.
Second, since two mechanisms have been used to individually provide resistance at the levers, an operator may experience a higher degree of resistance when actuating one lever than when actuating the other. With different resistance at each lever, one lever often returns to the neutral position more quickly than would be expected if both levers were set at the same level of resistance. In this case, it is often more difficult for a lever that has been released from a forward or rearward position to gradually return to its neutral position so as to allow the operator an ability to obtain control thereof. Consequently, the vehicle is often caused to be jerked from its travel direction when one of the levers is unexpectedly released, as previously mentioned.
Third, it has been difficult to adjust the resistance of both levers simultaneously and not affect the vehicle""s ability to maintain proper tracking. Tracking can be described as the ability of the vehicle to maintain a straight course when each lever is positioned in its furthest forward position so as to move the vehicle forwardly. Tracking has been set by adjusting the furthest distance the lever is permitted to move forwardly and rearwardly of its neutral position. Adjustment of the resistance has been made by either loosening or tightening the screws mentioned above to vary the distance that exists between the slide plates and the bottom portion of the mounting plates. Obtaining the same resistance setting at each of the levers has further been made difficult since maneuvering of the slide plates relative to the mounting plates has affected positioning of the pump arms. This affect occurs since each respective pump arm and its roller assembly is positioned between each slide plate and mounting plate and is therefore moved itself when an adjustment to the resistance at each of the levers is made. Consequently, adjustment of the resistance at each of the vehicle""s levers has been difficult to do without affecting its tracking. This difficulty exists since the mechanism(s) used to adjust the resistance is/are connected with the steering linkage(s) connecting each of levers to the respective pump arm(s).
Closely associated with the aspect of obtaining proper tracking is a fourth disadvantage regarding creep of the vehicle. Creep can be described as the tendency of the vehicle to move out of its neutral position. Setting of the neutral position has previously been done by adjusting the screws used to pre-load the spring mentioned above. These screws have been adjusted to obtain the neutral position for each of the pumps so as to bring the wheels of the vehicle to a stopped position.
Mechanisms such as those discussed thus far that adjust the resistance at each of the levers through setting of the amount of force placed on the pump arms often tend to cause the vehicle to creep. Creep of the vehicle has existed with these mechanisms because the slide plates and the pump arms contact each other when the levers are moved. To adjust the resistance at the levers, one has needed to affect positioning of the pump arms through the procedure described above. Disruption in this positioning has offset alignment in the neutral position previously obtained so as to cause the vehicle to not be able to obtain that position. As a result, the vehicle may move in an uneven or staggered pattern when moving from or returning to its neutral position.
Fifth, because there are two adjustment mechanisms, the cost of obtaining that same level of resistance when moving in the forward or rearward direction is expensive since separate components must be manufactured, installed and thereafter maintained.
Thus, it would be beneficial to provide an apparatus that permits an operator to simultaneously adjust the resistance experienced at each of the levers with minimal effort. Additionally, it would be beneficial to provide a single apparatus that permits the operator to obtain the same amount of resistance at each of the levers so as to steer the vehicle more effectively and do so with minimized cost.
Accordingly, there is provided a mechanism enabling an operator to easily adjust the resistance at the left and right levers at the same time. Also, there is provided a mechanism that allows the levers to gradually obtain a common neutral position allowing the operator to effectively steer the vehicle when starting from and returning to that position. Further, the mechanism is constructed with fewer components than structure previously used to set the resistance at both levers to thereby permit reduced costs of manufacture, installation and repair if needed.
To permit the vehicle to move, each of the levers is connected to a revolving sleeve mounted with the steering shaft that extends between the levers. Connected with the sleeves are two steering linkages, one for the left lever and one for the right lever, each having its opposite end connected to an arm extending from a respective left or right pump. Accordingly, upon movement of the levers, the sleeves are rotated to allow the arms to be moved so as to stroke or activate the pumps which then allows fluid to be released to the motors to cause the vehicle to move.
Control of the resistance at each of the levers is obtained by connecting the sleeves, and thus each lever, with a separate single adjustment mechanism. Specifically, the mechanism includes a left and right adjustment means in the form of an elongated bolt that connects the steering sleeves to a mounting plate coupled with the pumps. The mounting plate includes a bottom surface as well as front and rear walls. Each of the bolts is unsecured to the mounting plate and extends through a front wall thereof. The bolts continue and extend through a floating slide plate and include head portions which may abut against the slide plate depending on the position of each of the levers. Each of the bolts further includes a spring that is wrapped around a portion of the bolt which extends prior to the front wall of the mounting plate. Placement of the springs at that location permits them to be compressed against the front wall of the mounting plate when either the left or right lever or both is moved rearwardly. Setting of the amount of resistance experienced at either of the levers is accomplished through simply adjusting a nut coupled to either bolt and which holds the spring between the nut and front wall of the mounting plate. Accordingly, the resistance at each of the levers may be quickly adjusted since an operator need only access the nut and dial it along the bolt to obtain the amount of spring compression, and therefore the resistance that is desired for each of the levers.
When moved forwardly, resistance at each lever results from a center adjustment bolt positioned between the left and right adjustment bolts and which is secured to both the front and rear wall of the mounting plate. This center rod carries a spring thereon such that when the left and right levers are moved forwardly, the floating slide plate compresses against it as the heads on the ends of the left and right adjustment bolts opposite those connected to the steering sleeves will drag the slide plate toward the front of the vehicle. In doing so, the operator can obtain the same level of resistance when moving the left and right levers forwardly since only this center spring is placed in compression when both levers are moved forwardly. Likewise as in the case of setting the resistance at each of the levers in the reverse direction, a nut is used to establish the level of spring compression when the vehicle is moved forwardly. Accordingly, an operator may easily deliver the same level of spring compression for each of the levers thereby allowing the operator to obtain a synchronized amount of resistance for each lever to allow the vehicle to be more effectively steered in the forward direction.
To permit an operator to not affect the vehicle""s ability to track properly and also not cause it to creep, there is provided a mechanism that adjusts the resistance for each of the levers without being directly connected to the pump arms. This lack of structural connection between the adjustment mechanism and the pump arms permits resistance at each of the levers to be adjusted without affecting operation of the pumps, as described above. Accordingly, the vehicle may be steered more effectively since the pumps and structure associated therewith are operated independently of the resistance setting for each lever.
Additionally, since the resistance at both levers is separately controlled by the center rod and its associated spring when moved in the forward direction, the pace at which either lever returns to its neutral position is also separately controlled. Control of such pace is especially true when one lever is released and the other is maintained in the forward direction. In such a situation, the center spring will remain compressed against the slide plate as at least one lever is maintained in a forward stance. Thus, the spring along the rod with which the released lever is associated is permitted to gradually return the lever to the neutral position without affecting operation of the pumps since it is biased independently of the connection of the steering linkages to the pump arms. Consequently, the ability of the operator to obtain control of the lever that is suddenly released is increased so as to be more able to stop the vehicle from being abruptly diverted or jerked from an intended travel direction.
Thus, there is provided an adjustment mechanism for setting the resistance at the steering levers of an earth moving vehicle whereby the mechanism allows an operator to easily adjust the resistance of each lever to the same level at the same time in order to permit easy steering and control of the vehicle. Additionally, there is provided an adjustment mechanism that permits setting of the resistance at each lever with utilization of minimal parts permitting reduced costs of construction, installation and maintenance.